
Frank Marine
It lets a 7/8 inch tube sit into a 1 inch rail, which is the fix when you are joining gear built to different tube sizes. Common when adding a rod holder, a light bracket or a section of rail to a boat that already has fittings on it.
Outside diameter, every time. Rail sizes are quoted by the outside of the tube, so run a tape or calipers across the widest point and work from that. Guessing between 7/8 and 1 inch by eye is how people end up with a fitting that spins.
An adapter is a joiner, not a bracket. It bridges the size difference, but the load still has to go into a properly fastened rail and a solid mount underneath. Fasten through the tube rather than relying on a grub screw if there is leverage involved.

Frank Marine

Frank Marine

Frank Marine

Frank Marine

Frank Marine

Frank Marine
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